FRIDAY'S KILLER QUESTION: I have a revolver which holds up to six bullets....
Every Friday (starting today), we'll be posting challenging and cryptic questions for you to answer, provided for us by 7city Learning. Post your answers in the comments box at the bottom of the page. Maximum kudos will be provided to the person who provides the correct answer first.
We'll add the correct answer to the bottom of this article on Monday afternoon.
I have a revolver which holds up to six bullets. There are two bullets in the gun, in adjacent chambers. I am going to play Russian roulette (on my own!). I spin the barrel so that I don't know where the bullets are and then pull the trigger. Assuming that I don't shoot myself with this first attempt, am I now better off pulling the trigger a second time without spinning or spin the barrel first?
ANSWER:
Whenever you spin the barrel you clearly have a two in six or one in three chance of landing on a chamber containing a bullet. If you spin and pull the trigger on an empty chamber, what are the chances of the next chamber containing a bullet? You are equally likely to be at any one of the four empty chambers but only the last of these is adjacent to a chamber containing a bullet. So there is now one in four chance of the next pull of the trigger being fatal. Conclusion is that you should not spin the barrel. After surviving two pulls of the trigger without spinning the barrel the odds become one in three again, and it doesn't matter whether you spin or not (at least in the probabilistic sense). After surviving that 'shot' it becomes fifty-fifty and if you are successful four times in a row then the next shot will definitely be fatal.
